1. Field of the Invention
The present invention relates to an actuator for tilting a reflecting mirror of a digital micromirror device (hereinafter, referred to as “DMD”) for digital light processing (hereinafter, referred to as “DLP”) type projection, and, more particularly to an actuator for tilting a reflecting mirror of a DMD for DLP type projection that is capable of more accurately adjusting flatness of the reflecting mirror, which is tilted by the reflecting mirror tilting actuator according to the present invention, and of more conveniently performing flatness adjustment.
2. Description of the Related Art
Recently, large-sized high-definition displays have been increasingly popularized. For example, projection televisions and projectors have been developed and commercialized as the large-sized high-definition displays.
Each of the projection televisions and the projectors commonly includes an optical engine. In the optical engine is mounted a display unit for displaying signal-processed image information, such as a cathode ray tube (hereinafter, referred to as “CRT”), a liquid crystal display (hereinafter, referred to as “LCD”), a liquid crystal on silicon (hereinafter, referred to as “LCoS”), and a DMD.
A projection system adopting the CRT, which is usually used, forms desired images through very small bright cathode ray tubes and projects them through a lens. However, the CRT has several problems in that the brightness is low, adjustment of deflection based on frequencies is difficult, and adjustment of focus is difficult. As a result, the use of the CRT has been gradually decreased.
As the display units become miniaturized and lightened, a projection system adopting the LCD has been put on the markets, which is replaced with the projection system adopting the CRT, which is heavy and thick. In addition, other projection systems adopting the LCoS or the DMD have been put on the market or increasingly developed.
At present, LCD type projection systems are most widely used. However, the DLP type projection system using the DMD, which is excellent in realizing high contrast and fast in development speed as compared to the LCoS, which is advantageous in realizing high definition but slow in development speed, is now being developed and put on the markets.
The CRT and the LCD are display units that are driven by analog signals, and therefore, digital signals are converted into analog signals at the final signal-processing stage, and then the converted signals are displayed. On the other hand, the DMD is driven through pulse width modulation of digital signals without digital to analog conversion. Consequently, the DMD has the advantage in that errors generated during digital to analog conversion are minimized, and therefore, the DLP type projection systems using the DMD are in the spotlight of the recent projection systems.
FIG. 9 is a view illustrating the structure of a conventional DLP type projection system 1. As shown in FIG. 9, the conventional DLP type projection system 1 comprises: an illuminating optical system 1a; a reflecting type display unit 1b; and a projecting optical system 1c. 
The illuminating optical system 1a comprises: a light source 10; and an optical lens 20 for illuminating light output from the light source to the reflecting type display unit 1b. 
The light source 10 comprises: a lamp for generating light; and a reflector for reflecting the generated light to guide a route of the light.
The optical lens 20 comprises: a condensing lens 21 for condensing light output from the light source 10; and a shaping lens 23 for changing the condensed light into uniform light to shape the light in a predetermined pattern.
Between the condensing lens 21 and the shaping lens 23 is disposed a color wheel 22, which is rotated in one direction by a driving source (not shown) for selecting color light having a predetermined color and transmitting the selected color light. The color wheel 22 has a plurality of color filters, which are arranged in the circumferential direction of the color wheel 22 while being uniformly spaced apart from each other.
The display unit 1b, to which the light output from the illuminating optical system 1a is illuminated, comprises a DMD 30. The DMD 30 is mounted on a substrate 33, on which a processor 31 and a memory 32 are also mounted. The DMD 30 serves to separate a light route of the illuminating optical system 1a from a light route of the projecting optical system 1c based on tilting angles.
The DMD 30 is a projection type display unit using an optical semiconductor, which has been developed by Texas Instrument Incorporated in the United States of America. Specifically, the DMD 30 comprises a plurality of reflecting mirrors, each having a very small size, disposed on a silicon wafer in two dimensions. Each reflecting mirror corresponds to each pixel. The DMD 30 controls the light reflected by the reflecting mirrors to display pictures.
Each reflecting mirror is tilted by a reflecting mirror tilting actuator at high frequency, for example, tilted every 10 μs, for switching an incident light route between two states (ON and OFF) to reflect the incident light.
When the reflecting mirror corresponding to each predetermined pixel is tilted by the reflecting mirror tilting actuator such that the reflecting mirror is in the ON state, the light reflected by the reflecting mirror is magnified through a projection lens 40 of the projecting optical system 1c to illuminate the magnified light onto a screen 50. When the reflecting mirror is tilted by the reflecting mirror tilting actuator such that the reflecting mirror is in the OFF state, on the other hand, the light reflected by the reflecting mirror is away from the projection lens 40 of the projecting optical system 1c with the result that the light is not illuminated onto the screen 50.
Consequently, the digital micromirror device 30 changes the reflecting angle of the light by independently tilting the reflecting mirrors according to an image signal based on each pixel to turn the light ON/OFF, and illuminates the images magnified by the projection lens 40 onto the screen 50 in large size.
The reflecting mirror tilting actuator tilts the reflecting mirror to a tilting angle of from approximately −10 to +10 degrees in a cycle of 60 Hz to guide the light reflected on the reflecting mirror to a predetermined direction. At this time, it is necessary that flatness of the reflecting mirror be accurately adjusted to below 1.2 μm.
After assembly of the reflecting mirror and the reflecting mirror tilting actuator is completed, however, it is difficult to accurately adjust flatness of the reflecting mirror to below 1.2 μm. Furthermore, flatness adjustment is very difficult.